1. Field of the Invention
The present invention relates to an antenna structure and a communication apparatus, and more specifically to an antenna structure and a communication apparatus for enhancement of the spatial efficiency of an antenna.
2. Description of the Related Art
An antenna adaptive to a 2G (second-generation mobile telephone), a 3G (third-generation mobile telephone), etc. has been proposed by a conventional communication apparatus such as a mobile telephone, etc. due to improved functions of the mobile telephone (refer to Patent Document 1: Japanese Patent Laid-Open No. 11-340731).
The 2G refers to a second-generation mobile telephone, and corresponds to a PDC (personal digital cellular) system or a GSM (global system for mobile communication) system, etc. using digital technology. The second-generation mobile telephone uses a frequency band of 800 to 900 MHz.
The 3G refers to a third-generation mobile telephone, and corresponds to a CDMA (code division multiple access) system, etc. A part of the third-generation mobile telephones use a frequency band of about 1.5 GHz.
The above-mentioned Patent Document 1 proposes a non-feed antenna capable of independently adjusting a plurality of frequencies with a small coupling loss between antennas. That is, the non-feed antenna is a built-in antenna for a plurality of frequencies, and saves space.
In detail, the above-mentioned Patent Document 1 proposes the following configuration. That is, a wireless device has the built-in antenna and a feed antenna arranged outside the wireless device. The outside feed antenna transmits and receives radio waves (electric waves). The built-in antenna, namely the non-feed antenna includes two antennas, that is, a first antenna and a second antenna, and a feeder for interconnection between them. Each of the feed antenna of the wireless device and the first antenna of the non-feed antenna is configured by a loop antenna. Each antenna is located close to each other firmly in a capacitive coupling status. Therefore, the antenna of the wireless device and the first antenna communicate radio wave with each other by the electromagnetic induction through the capacitive coupling (refer to Patent Document 1, paragraph [0044]).
Another prior art is formed by a substrate, a first antenna element provided on one of the right and reverse sides of a sheet or a sheet member, and a second antenna element provided on the other side (refer to Japanese Patent 2: Application Laid-open No.2002-111348). The Patent Document 2 proposes a small antenna capable of easily presenting a frequency response of a broad band.
If the above-mentioned mobile telephones of the respective, generations are incorporated as a complex structure, a plurality of antennas is required. In this case, a small wireless device of a mobile telephone, etc. has the difficulty in incorporating two or more antennas into the wireless device, thereby causing a bottleneck in the development.
That is, a communication apparatus to which antennas are applied has become smaller and thinner. Therefore, in the above-mentioned communication apparatus, an antenna or a communication apparatus is to be downsized to enhance the practicability and operation efficiency.
The present invention aims at providing an antenna structure and a communication apparatus with the spatial efficiency and the utilization improved.